In electrophotography, an image forming method typically uses a photoconductive substance to form an electrostatic latent image on an electrostatic image carrying member using various means. The electrostatic latent image is then developed with toner and is transferred on a recording sheet and the like as desired. Subsequently, the toner is fixed by heating or solvent vapor so that copy images or printed images can be obtained. For developing latent electrostatic images formed on an electrophotographic image carrier such as a photoconductor to visible toner images, there are conventionally proposed two methods: a wet-type developing method using a liquid type developer, and a dry-type developing method using a dory-type developer. The dry-type developer includes a one-component dry-type developer comprising a toner obtained by dispersing a coloring agent such as a colorant in a binder resin; and a two-component dry-type developer obtained by mixing the above-mentioned toner and carrier particles. Although these methods individually have their own advantages and shortcomings, the dry-type developing method is more prevalent than the wet-type developing method.
Since in the two-component developing method it is relatively easy to increase operation speed and lengthen lifetime as compared with the one-component developing method, the two component developing method is widely used for medium and high speed copiers and printers.
For carrying out the above-mentioned developing method, the developing device employs the two-component developing method for controlling toner concentration using two developer regulating members and a developer carrier. This system eliminates a sensor and a toner supply controlling device, thereby making a device relatively inexpensive and compact.
The above-mentioned developing device, however, has several disadvantages. One disadvantage is that it prevents a compulsive toner supplying control. As a result, a toner concentration control depends on a gap between a regulating member and the developer carrier, a gap between a developer stirring member and the developer carrier, and magnetic flux density caused by a magnet of the developer carrier, and a peak magnetic flux density and a position of one half band width (i.e., angle) of the developer carrier.
However, assembling deviations caused by a regulation gap of the two regulating members (i.e., first and second regulating members), manufacturing precision and tolerances of parts, and magnetic flux density deviation caused by a magnet of the developer carrier cause an amount of the developer regulating deviation. Therefore, the developer tends to be axially located in a longitudinal direction of the developer carrier. This causes the developer to be nearer one end of a development region. An increase in the developer at one end decreases toner, thereby causing a loss in image concentration. A decrease in the developer at one end increases toner, thereby causing a soiling of background.
Further, the two-component developing device with a toner concentration controlling function can be downsized so that it can be utilized for a compact printer and the like. The compact printer is often placed on a desk so that the printer tends to be operated in an inclined position as compared to a large printer placed on a floor. Such an inclined printer tends to make the developer move to one end. This leads to a loss in latent image concentration and a soiling of background at one end.
Therefore, a high parts tolerance and assembly precision are demanded in this system. Utilizing a machine in a horizontal position is required. As long as the above-mentioned condition is not satisfied, unusual images such as uneven image concentration and a soiling of background tend to be generated.